1. National Institute for Research and Development in Microtechnologies (IMT Bucharest), 126A Erou Iancu Nicolae Street, 72996 Bucharest, Romania
2. Faculty of Physics, University of Bucharest, P.O. Box MG-11, 077125 Bucharest, Romania
3. Faculty of Applied Chemistry and Material Science, University Politehnica of Bucharest, No. 1-7 Gh. Polizu Street, 011061 Bucharest, Romania